Heretofore, radiation images such as X-ray images have been widely applied to diagnosis of the state of a disease in medical settings. In recent years, digital system radiation image detectors, represented by a flat panel type radiation detector (FPD) have appeared, whereby it is now possible to process radiation images without limitation upon obtaining as digital information and to instantaneously transmit such image information.
With regard to the FPD, a scintillator panel is employed, which emits fluorescence instantaneously when received radiation which is transmitted through a subject at an intensity in accordance with the amount of the radiation. The light emission efficiency of the scintillator panel increases with the thickness of the phosphor layer. However, when the phosphor layer is excessively thick, the contrast of images is lowered due to the scattered light generated within the phosphor layer. High contrast images are essential for effective diagnosis.
When columnar crystal structured phosphors such as cesium iodide (CsI) are employed, generation of scattered light within the crystal is decreased due to a light-guiding effect, whereby it is possible to enhance light emission efficiency in such a state that the contrast is retained by increasing the thickness of the phosphor layer. Further, it is also possible to enhance light emission efficiency by incorporating elements such as thallium (Tl) as an activator into cesium iodide (CsI). (refer, for example, to Patent Document 1)
Usually a protection cover is provided on the radiation incident side of a scintillator panel to protect the scintillator panel against external impact. In addition, a light-receiving element which receives light emitted from the scintillator panel is provided on the opposite side of the protection cover of the scintillator panel. Further, a cushioning member is arranged between the scintillator panel and the protection cover so that the cushioning member brings the scintillator panel into appropriate contact with the flat light-receiving element so that the scintillator panel is brought into pressure contact with the light-receiving element at an appropriate pressure by pressure from the compressed cushion element when a protection cover is furnished.
When a radiation image detector is assembled, a scintillator panel and a cushioning element are sequentially placed on the light-receiving element arranged within the cabinet, followed by fixing the protection cover to the cabinet with such as screws.
In such a case, when pressure applied to the cushioning member is excessively high, the tips of phosphor crystals of columnar crystal structure are modified to result in a decrease in the contrast of radiation images. On the contrary, when the pressure of the cushioning member is too low, the scintillator panel is not sufficiently brought into contact with the flat light-receiving element while the FPD is directed downward, whereby the contrast of radiation images is adversely lowered. Further, due to friction between the scintillator panel and the flat light-receiving element via shifting or vibration of the FPD, defects apparently tend to occur in the flat light-receiving element or within the phosphor layer.
In general, a phosphor layer thickness of at least 400 μm is necessary to prepare radiation images with targeted graininess. However, the increase in weight or size of the scintillator panel due to the increase in layer thickness results in problems more serious than those described above.
To solve these problems, various methods have been proposed which include a method to fix the scintillator panel and the flat light-receiving element with adhesives (for example, refer to Patent Document 2), and a method to allow the scintillator panel to adhere to the flat light-receiving element by employing matching oil (refer, for example, to Patent Document 3). These methods, however, have problems such as generation of unevenness of the adhesives or the matching oil, and an increase in operation man-hours.
(Patent Document 1) Japanese Patent Publication Open to Public Inspection (hereinafter referred to as JP-A) No. 2002-116258
(Patent Document 2) JP-A No. 2006-189377
(Patent Document 3) JP-A No. 2000-9845